Liquid crystal displays find use in a variety of different applications, such as data displays in watches, calculators and the like, as well as in flat panel displays found in laptop or notebook computers. Liquid crystal displays offer many advantages over alternative technologies, e.g. cathode ray tube based displays, where such advantages include: low power consumption, small size, light weight, and the like. As such, it is believed by many that liquid crystal displays will find wide-spread use in an even larger number of different applications than those in which they currently find use, where it is envisioned that liquid crystal displays will eventually become standard features in desktop computer monitors, televisions, etc.
In typical flat panel displays currently found in many laptop computers, the picture on the screen of the display is composed of many pixels whose size depends on the product. For example, the current 12.1 inch SVGA displays have pixels of approximately 300.times.300 .mu.m in size. In each pixel the desired color is created by "mixing" blue, green and red primary colors of different intensities by means of having patterned color filters of these three colors on separate electrodes. The intensity of each color is adjusted by using liquid crystals to change the light intensity transmitted from the back to the front of the display. The liquid crystal (LC) is composed of rod-like molecules that tend to keep their long axis aligned due to intermolecular forces. The LC is filled into the gap, a few microns wide, between two polyimide films coated onto indium-tin-oxide electrodes which, in turn, are deposited onto two glass-plate polarizers. In order for the display to work, the LC molecules have to be anchored down nearly parallel to the surfaces of the polyimide films but on opposite sides point into the perpendicular directions of the two crossed polarizers. The LC molecules thus form a twisted helix from one side to the other. When light from a light source in the back of the display crosses the first polarizer it is polarized along the long axis of the LC molecules anchored to it. As the light progresses through the LC, the helical LC structure changes the polarization of the light from linear to elliptical so that only part of the light is transmitted by the second, perpendicular polarizer. Since the light transmission depends on the orientation of the LC rods it can be changed by rotation of the long axis of the LC rods. This is accomplished by application of a small voltage to each color cell within all pixels by means of microscopic indium tin oxide (ITO) electrodes independently driven by a transistor array. As the voltage is increased, the LC long axis becomes increasingly parallel to the electric field direction, which is parallel to the light transmission direction. The light polarization becomes less affected by the LC and the light transmission is reduced because of the crossed polarizers.
A display is said to be "single domain" if the LC molecules have a single pre-tilt angle along one azimuthal direction of the surface plane (i.e. the long axis of the LC molecules is orientated along in-plane direction and tilted up from that direction by a well defined angle which, in the case of current 12.1 inch SVGA displays, is a few degrees) and hence long axes of all LC molecules appear more or less parallel to each other over the whole display. A multi-domain display contains at least two differently oriented single domain regions such that the two or more single domain regions form a color sub-pixel of the display. A drawback of many currently employed single-domain liquid crystal displays is that such devices are characterized by having a narrow or limited viewing angle. As such, a number of different methods have been developed for producing multi-domain liquid crystal displays. Such methods include the mask rubbing two domain method (JP-106624), the fringe field two domain method (U.S. Pat. No. 5,309,264), the double alignment layer two domain method (Koide et al., SID 92 Dig. (1992) 798) and the UV treatment two domain method (Lien et al., Appl. Phys. Lett. (1995) 67:3108). Yet another approach to improving the viewing angle of liquid crystal displays has been to employ a textured alignment layer. See Nikkei, Flat Panel Display (1998) 104 to 107.
Despite the development of the above methods for producing multi-domain liquid crystal displays, there continues to be an interest in the development of new methods of producing multi-domain displays with broad viewing angles. Ideally, such methods should have a minimal number of steps, be efficient and be adaptable to clean-room high throughput manufacturing.
Relevant Literature
U.S. Pat. Nos. 5,757,455; 5,721,600; 5,717,474; 5,657,105; 5,608,556; 5,576,862; 5,550,662; 5,508,832; 5,479,282; 5,410,422; 5,309,264 describe multi-domain liquid crystal displays.